Artificial sweeteners linked to cognitive decline

Low- and no-calorie sweeteners (LNCSs), such as aspartame and saccharin, have become part of daily life for millions of people. Found in diet sodas, protein powders and sugar-free snacks, these sweeteners deliver sweetness without calories or spiking blood sugar levels, making them marketable for people trying to cut back on sugar or manage conditions such as type 2 diabetes. New research, however, sheds light on the possible effects of LNCSs on cognitive function, finding that their consumption may be associated with accelerated cognitive decline.

Researchers in Brazil (Gonçalves et al., 2025) investigated the effects of LNCSs on the cognitive function of 12,772 civil servants. The cohort, aged 35 and older, and comprising 54.8% women, was studied for a period of 8 years. Dietary intake of LNCSs was measured using a Food Frequency Questionnaire, capturing their daily consumption of seven sweeteners: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose. Cognitive performance was assessed using six standardized tests covering domains such as verbal fluency, working memory, word recall, and processing speed. To understand how intake levels related to cognitive outcomes, participants were divided into three groups based on daily consumption. The lowest group consumed an average of 20 mg, and the highest group consumed an average of 191 mg per day.  For comparison, a single can of Diet Coke contains around 188-200 mg of aspartame. 

"Some sweeteners may contribute to neurodegeneration by elevating cortisol levels, and increasing the production of free radicals, causing oxidative stress"

Across the cohort, the average daily intake of LNCSs was 92 mg, with sorbitol being the most consumed sweetener (64 mg/day). Those in the highest consumption group experienced a 62% faster decline in cognitive function, especially in memory and verbal fluency, compared to the lowest group. The study also revealed that not all sweeteners have the same effect. Six of the seven studied — aspartame, saccharin, acesulfame-K, erythritol, xylitol, and sorbitol — were linked to measurable declines in cognition. Tagatose, on the other hand, showed no significant association with cognitive decline.

The impact of LNCSs also varied by age. Among participants younger than 60, higher consumption was consistently linked to cognitive decline; in older subjects, no significant relationship was observed. Diabetes status further influenced the outcomes, revealing that cognitive decline was faster in individuals suffering from diabetes, who often use artificial sweeteners as a replacement for sugar.

While this study alone cannot prove that LNCSs cause cognitive decline, scientists have proposed several mechanisms that could explain the results. One possibility is that sweeteners alter the gut microbiome, causing a decrease in beneficial bacteria and an increase in harmful ones. This has been linked to inflammation and neurodegeneration, as it affects the gut-brain axis and the production of neurotransmitters. Another potential mechanism involves the way sweeteners are metabolised. Aspartame, for example, breaks down into aspartic acid and phenylalanine, compounds that in high amounts can disrupt neurotransmitter balance. This could affect levels of dopamine, serotonin, and norepinephrine, which are essential for memory, learning, and mood regulation. Additionally, some sweeteners may contribute to neurodegeneration by elevating cortisol levels, and increasing the production of free radicals, causing oxidative stress . Both processes are linked to cell damage and may result in the death of brain cells, having an impact on brain function and cognition.

"Those in the highest consumption group experienced a 62% faster decline in cognitive function"

This research, however, has its limitations. Dietary intake was self-reported, which could result in under- or over-estimation of their LNCS consumption. Furthermore, the study could not fully account for other lifestyle factors such as exercise, overall diet quality, or alcohol use, all of which may also influence cognition. While the study covered a large and diverse sample, it only investigated seven sweeteners, and results may not apply to others that were not studied. This is important as the study showed that not all sweeteners behave the same way.

The findings also raise important questions about the long-term safety of artificial sweeteners. While LNCSs are often promoted as healthier substitutes for sugar, the results suggest that high consumption may come with unintended consequences for cognitive health. The observation that younger adults and people with diabetes were most affected is especially concerning, given that these groups are among the most frequent consumers of sweetened products. For policymakers and healthcare professionals, the study highlights the need to reconsider current dietary recommendations around artificial sweeteners. It also highlights the importance of further research to establish whether the associations observed reflect true causal effects.

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This article was written by Giulia Lima and edited by Julia Dabrowska, with graphics produced by Ishika Joshi. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.